Identification of PARP-1 as one of the transcription factors binding to the repressor element in the promoter region of COX-2.

Cyclooxygenase-2 (COX-2) plays important roles in the development of many disease conditions, including pancreatic β-cell dysfunction. Although the processes involved in the transcriptional regulation of COX-2 are well documented, some key elements, especially inhibitory elements, are still unknown. In our previous study, we identified a novel repressor element located in promoter region of mouse COX-2. In this study, we isolated several DNA-binding proteins from NIT-1 cells via DNA affinity chromatography; the most prominent among these proteins was poly (ADP-ribose) polymerase-1 (PARP-1). In this study, gel-supershift assays and chromatin immunoprecipitation assays showed that PARP-1 can bind to the inhibitory element -655/-632 in the promoter region of mouse COX-2 both in vitro and in vivo. Furthermore, overexpression of PARP-1 significantly inhibited promoter activity and decreased COX-2 expression. Conversely, repression of PARP-1 by RNAi upregulated COX-2 expression. These data suggest that PARP-1 plays an important role in the regulation of COX-2 expression via binding to the inhibitory element. Collectively, our findings provide new important information on the transcriptional regulation of COX-2 in pancreatic β-cells.